Comparison of active flow control devices on bluff body shapes

Abstract

Results from experimental studies on the performance of plasma and synthetic jet actuators for active control of flow over a circular cylinder in subcritical flow conditions ranging from a Reynolds Number of 2.5 x 10 4 to 7.3x10 4 are presented. The experiments were conducted at the NASA Langley Research Center in the 20 x 28 Shear Flow Wind Tunnel and the results provide an indication of the effectiveness of, as well as the similarities and differences between these two active flow control (AFC) methods for reducing pressure drag on a bluff body shape. Flows over a cylinder are well understood and in particular flow separation characteristics for cylinders are well documented both experimentally and theoretically. The effect of the flow control devices is quantified by measuring the pressure distribution around the bluff bodies using a multi-port piezoelectric pressure scanner and integrating the distribution for drag analysis. This comparison consists of operating the two types of actuators in the same range of Reynolds Numbers (Re) over the cylinder and for the same actuator angular positions on the cylinder. The applied voltages and frequencies to the actuators varies based on the individual actuator operating conditions. At low Re, the plasma actuators have a strong effect on the pressure distribution reducing the drag up to 32% relative to the drag with no actuators on the surface. The synthetic jet reduces drag up to 25% but with lower voltage and frequency. For both actuator cases, the actuator is the most effective 5° to 10° upstream of the baseline separation point.